The peripheral sensory innervation of the face and mouth is often injured by accidental (eg, maxillary and mandibular fractures) and iatrogenic (eg, orthognathic, preprosthetic and implant surgeries) insults. Although most patients recover sensation, a significant number report with permanent sensory dysfunction. Moreover, the magnitude of the problem is unclear since conventional neurosensory tests are thought to identify only gross deficits. Unfortunately, there are no current means by which subtle degrees of sensory impairment can be detected, quantitated, and assessed during the period of recovery. Given that a large body of clinical and neurophysiological data suggests that tests which employ moving tactile stimuli may provide optimally sensitive indicators of neurosensory function, we propose to evaluate a validated psychophysical test of direction discrimination capacity for clinical use. The test to be employed estimates a patient's capacity to distinguish opposing directions of tactile motion, and provides quantitative measures of (i) maximum directional sensitivity at the test site, (ii) the velocity of stimulus motion at which maximum sensitivity is predicted to occur, and (iii) the degree to which directional sensitivity is influenced by changes in stimulus velocity. Normative limits (ie, upper and lower 2.5% points) for each of four quantitative indices which characterize direction discrimination will be established. Twenty different sites on the faces of young adult males and females will be studied. In order to assess whether direction discrimination is impaired after different degrees and types of peripheral nerve damage and after different periods of recovery, patients who are candidates for either orthognathic surgery or nerve exploration/repair procedures will be evaluated preoperatively, and at, 1, 6 and 12 months, postoperatively. It will also be determined whether the area (ie, spatial extent) of impairment in nerve-injured patients is greater when determined by tests of direction discrimination than by conventional tests of low- threshold mechanoreceptor function (ie, """"""""von Frey tests"""""""" and tests of the 2-point threshold). In order to better appreciate the impaired discriminative capacities of nerve-injured patients, simulations of the disordered spatiotemporal patterns of afferent discharge activity believed to accompany peripheral nerve injury will be investigated. Specifically, novel moving stimuli will be delivered to normal skin to elicit altered patterns of mechanoreceptor activity. The patterns to be employed should mimic the altered patterns of peripheral neural input which are elicited in damaged nerves by natural moving tactile stimuli.
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